/* postgres can not */
/* syntax version 1 */
pragma OrderedColumns;

select 1 as z, 2 as y, 3 as x
union all
select 1 as z, 2 as y
union all
select 1 as z;

select 1 as z, 2 as y, 3 as x
union all
select 1 as z, 2 as y
union all
select 1 as a;